Impedance cardiography in uncomplicated pregnancy and pre-eclampsia: correlation between diurne- and

Impedance cardiography in uncomplicated pregnancy
and pre-eclampsia: correlation between diurne- and
position-challenged measurements
Kathleen TOMSIN
Tinne MESENS
1
, Geert MOLENBERGHS
1,2
2
,
, Wilfried GYSELAERS
1,2
1. Ziekenhuis Oost-Limburg, Genk, Belgium
2. Hasselt University, Diepenbeek, Belgium
Short title: ICG in pregnancy
Keywords: Hemodynamic Monitoring, Non-Invasive Method, Correlation Coefficient,
Diurnal Variation, Postural Challenge
Correspondence:
Kathleen TOMSIN
Department of Obstetrics and Gynaecology, Ziekenhuis Oost-Limburg
Schiepse Bos 6, 3600 Genk, Belgium
Telephone: (032)89 32 75 24
Fax: (032)89 32 79 20
E-mail address: kathleen.tomsin@zol.be
1
Abstract
Background/Aims: To evaluate intra- and intersession correlation of Impedance
Cardiography (ICG) measurements after orthostatic and diurnal challenges in three
clinical situations: uncomplicated pregnancy, pre-eclampsia and cardiovascular disease.
Methods: Twice in one day (AM and PM), a standard protocol was used to record ICG
measurements before and after three position changes in uncomplicated third trimester
pregnancy, pre-eclampsia and cardiovascular disease (n=10 each). A total of 22
cardiovascular parameters was measured, classified in five groups:
pressures, time
periods, volumes, contractility and resistance. For each parameter, Pearson’s correlation
coefficient (PCC) was calculated for mean values of 30 measurements per position per
subject. Intra-session PCC was used to correlate position-challenged measurements,
whereas inter-session PCC was used to correlate AM and PM values.
Results: In all populations, intra- and intersession PCC was consistently ≥ 0.80 for three
contractility parameters (acceleration-, velocity- and heather-index). This was also true
for thoracic resistance parameters in uncomplicated pregnancy and pre-eclampsia.
Conclusion: Our data illustrate that correlation between diurne- and orthostaticchallenged ICG measurements of cardiac contractility is high under standardised
conditions in normal pregnancy, pre-eclampsia and cardiovascular disease. As such, ICG
is a useful method to study changes of cardiac (dys)contractility in pregnancy and preeclampsia.
2
Introduction
Human pregnancy is characterised by major cardiovascular adaptations, such as plasma
volume
expansion,
reduced
vascular
resistance
and
increased
heart
rate
[1].
Maladaptation of the cardiovascular system plays a significant role in the pathophysiology
of pre-eclampsia, a disease associated with significant morbidity and mortality for both
mother and child. It has been reported that cardiac contractility is altered in preeclampsia
compared
to
normal
pregnancy
[2-6].
Current
methods
to
evaluate
cardiovascular (mal)adaptation during pregnancy have not gained popularity because of
their invasive nature [7-9] or the lack of required expertise [10].
Impedance
cardiography
(ICG)
is
designed
for
non-invasive
measurement
and
monitoring of cardiovascular parameters on a beat-to-beat basis. ICG enables a
continuous parallel registration of multiple parameters in a single session [11-13]. Good
correlation between diurne- and position-challenged ICG measurements was reported in
healthy non-pregnant subjects, especially when mean values of multiple measurements
were used for each parameter [14].
We evaluated intra- and intersession correlation
of ICG measurements for 22
cardiovascular parameters with a third generation device after orthostatic challenge and
between morning- and afternoon-sessions in women with uncomplicated third trimester
pregnancy, women with pre-eclampsia and cardiovascular diseased patients.
3
Materials and Methods
Approval of the local ethical committee was obtained before study onset (MEC ZOL
reference: 09/050). Three populations of each ten randomly selected subjects were
included: pregnant women in normal third trimester gestation (UP) presenting at the
antenatal clinic of the department of obstetrics and gynaecology in Ziekenhuis OostLimburg, Genk, Belgium, and women with pre-eclampsia (PE) admitted to the Unit for
Fetomaternal Medicine in the same hospital. A third group of critically-ill cardiology
patients, admitted to the cardiovascular intensive care unit (CV) was also included as a
reference and control group. PE was defined according to standard criteria [15]:
gestation induced hypertension > 140/90 on at least two occasions 6 hours apart, in
combination with > 300 mg proteinuria per 24 hours.
Data collection
The ICG system used in this study is the Non-Invasive Continuous Cardiac Output
Monitor (NICCOMO™, Software version 2.0, SonoSite, Medis Medizinische Messtechnik
GmbH, Ilmenau, Germany) with a four electrode arrangement eliminating skin
resistance. This system allows for simultaneous measurement of 22 parameters in five
categories: pressure, time period, volume, contractility and resistance parameters
[14;16]. The examination was performed according to the protocol as reported [14].
After informed consent, for each subject, a consecutive series of ICG-examinations in
different positions were performed during normal breathing (Figure 1): (1) supine 1, (2)
standing, (3) sitting and (4) supine 2. To evaluate possible influences of the circadian
rhythm, this series of measurements was performed at morning (AM) and in the
afternoon (PM).
During the sessions, ICG values were recorded every two seconds, and blood pressure
was taken automatically every two minutes. Per position, blood pressure was measured
4
twice. Data were collected over a timespan of one minute after the second blood
pressure value was depicted on the screen. These values were neither influenced by the
blood pressure measurement itself nor the movements during change in position.
Data were exported from the monitor into a database: for every position during each
session, one value for pressure parameters and 30 values of other parameters were
eligible for analysis.
Statistical analyses
For each parameter, Pearson’s correlation coefficient (PCC) was calculated for mean
values of 30 measurements per position per session per subject. Intersession correlation
was evaluated between supine 1 AM and supine 1 PM, between standing AM and standing
PM, between sitting AM and sitting PM and between supine 2 AM and supine 2 PM.
Intrasession correlation was evaluated between positions supine 1 and supine 2 per AM
or PM session.
5
Results
Patient characteristics of the three study populations are enlisted in Table 1. Mean age
was
32.70±3.30,
30.12±6.05
and
68.64±14.51
years
for
normal
pregnancy,
preeclampsia and cardiovascular disease respectively. The time interval between AM and
PM sessions was 05:50:36 ± 01:13:08 h.
Table 2 and Table 3 represent inter- and intrasession Pearson’s correlation coefficients
(PCC). The contractility parameters acceleration index, velocity index and heather index
consistently showed PCC ≥ 0.80 in the three groups. This was also true for thoracic fluid
content and -index in healthy and pre-eclamptic pregnant women, but not for
cardiovascular patients (PCC ≥ 0.60). For time periods heart rate and heart period
duration, and all volume parameters, PCC was higher in cardiovascular patients (≥ 0.80)
than in both healthy and pre-eclamptic pregnant women (< 0.60). For other parameters,
PCC was < 0.6 on at least one occasion.
6
Discussion
Measurements by ICG are reliable as they correlate highly with standard methods [1722], however imprecise ICG in severely ill patients was reported [13;23]. In healthy nonpregnant subjects, we observed that position-induced changes of ICG measurements are
independent from the time of day for time period, volume, contractility and thoracic
impedance [14]. We also found that reproducibility of ICG measurements was much
better when mean values of multiple measurements were used for each parameter [14].
Non-invasive assessment of the cardiovascular system and cardiac contractility is
relevant to explore maternal gestational adaptation mechanisms, as well as background
mechanisms behind cardiovascular diseases. We used the same study protocol as
reported [14] to evaluate ICG measurements in uncomplicated pregnancy, during preeclampsia and in cardiovascular disease.
As shown in Table 2 and Table 3, inter- and intrasession correlation was high for
contractility parameters and thoracic fluid content in normal pregnancy and preeclampsia. This was different from patients with cardiovascular disease, where
correlation coefficient for these parameters were lower.
Cardiac adaptation is an important feature of maternal cardiovascular changes during
pregnancy. The increased preload during normal gestation induces a reversible
remodeling of the heart, i.e. left ventricular eccentric hypertrophy, together with a wellpreserved left ventricular systolic function [2;24]. The latter probably results from
enhanced relaxation of the left ventricle at the start of diastole, probably due to
hormonal influences [2]. In pre-eclampsia however, an increased afterload results in left
ventricular
concentric
hypertrophy
[2;3;25],
a
condition
often
associated
with
unfavorable outcome and extracardiac target organ damage [4;26]. Pre-eclampsia is not
only associated with this type of heart remodeling but also with significant changes in
cardiac function: systolic but even more diastolic function are impaired [2-5;27].
7
Concentric hypertrophy occurs when there is a pressure overload, volume underload and
diastolic dysfunction [4], all of which are often present during pre-eclampsia [25;25;27]. These features may persist after pre-eclampsia, predisposing to hemodynamic
maladaptation to subsequent pregnancy and recurrence of pre-eclampsia [5]. Highly
reproducible ICG measurements for contractitily parameters acceleration-, velocity- and
heather index indicate that impedance cardiography is an appropriate tool to conduct
cardiac contractility studies in pregnancy and preeclampsia.
Thoracic resistance parameters TFC and TFCI also showed high reproducibility in normal
and pre-eclamptic pregnancy (Table 2 and Table 3). TFC is a measure of total thoracic
fluid content, both intra- and extracellular, which can be measured reliably with ICG
[19]. This parameter is for detection of subclinical signs of congestive heart failure in the
early stages of pulmonary edema [28;29]. In pre-eclampsia, higher TFC values have
been observed in severe than in mild disease [16;30]. At values  65 kohm-1, the relative
risk for development of pulmonary edema in peripartum was 18.2 relative to women with
lower values [30]. Our results show that ICG may also be a valuable method to assess
early stages of pulmonary edema in PE.
Intra- but even more intersession correlation for blood pressure parameters was variable.
Diurnal variation for maternal blood pressure has been reported, together with diurnal
variation for heart rate [31]. For time periods and volume parameters, intra- and
intersession correlation coefficients were lower in pregnancies than in cardiology patients
(Table 2 and Table 3) and in healthy subjects [14]. This may relate to the pregnancyassociated inability to regulate heart rate and blood pressure in response to postural
alterations [32;33], and increased gestational variability of heart rate and blood pressure
[34] which is even higher in pregnancy-induced hypertension [35]. Contrary to
observations from others, we found in an heterogenous population of CV patients highly
reproducible
ICG
measurements
for
contractility,
time
and
volume
parameters
[13;23;36], which may relate to the specific set-up of our protocol.
8
From the data presented in Table 2 and Table 3, we conclude that ICG measurements of
cardiac contractility and thoracic fluid content using a third generation device in healthy
and pre-eclamptic pregnant women correlate well after diurnal- and position-induced
challenge. Because normal and pathologic change of cardiac contractility has been
reported during pregnancy, our results open perspectives to implement impedance
cardiography as a non-invasive method to study (mal)adaptation of cardiac contractility
in normal pregnancy and in pre-eclampsia.
Acknowledgements
The authors would like to thank Wilfried Mullens (MD, PhD) of the cardiovascular
intensive care unit and Louis Peeters (MD, PhD) of the Maastricht University Medical
Centre for their kind help and recommendations in our study.
9
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12
Tables
Table 1. Patient characteristics of the three study populations: normal third trimester
pregnant women (UP), women with pre-eclampsia (PE) and critically-ill cardiology
patients (CV).
NP
PE
Gestational age
Age
P
(weeks)
Exam
Delivery
30,5
P1
33,9
37,0
P4
28,5
P1
29,1
CV
Gestational age
Age
P
(weeks)
Exam
Delivery
36,4
21,1
P0
30,6
31,1
29,1
40,1
25,9
P0
31,7
35,3
39,4
30,0
P0
34,0
P0
32,9
40,7
25,5
P0
38,0
P2
28,4
39,1
36,9
32,2
P1
29,1
38,3
32,2
32,3
P2
27,3
35,3
35,2
P1
31,9
34,2
P1
36,7
30,0
P0
33,4
ProtU
Age
Sex
Disease
2543
42,2
M
CD4, CD5, non-STEMI
32,1
838
82,9
F
HF, V, SD, PD
34,1
7823
84,3
F
CD1, CD2, HF
32,1
32,4
7053
59,5
M
STEMI, CAD
P1
24,9
26,6
336
73,7
M
CD1, V, CAD
P1
36,6
36,9
2115
74,3
F
Aortic Dissection
35,4
P0
38,9
40,0
589
84,2
M
CD1, HF, PD
38,4
40,5
P0
36,9
39,0
310
62,4
F
CD1, SD, HF, PD
40,9
27,2
P0
39,7
40,0
10255
72,0
F
CAD, SD, HF, PD
36,9
26,3
P0
36,7
36,9
515
50,9
M
STEMI
(mg)
P: Parity; ProtU: Proteinuria (mg/24h); Sex: M=Male, F=Female; STEMI: ST Elevated Myocardial Infarction; V:
Valve disease; SD: Systolic Dysfunction; HF: left or right-sided decompensated Heart Failure; PD: Pulmonary
Disease (pulmonary edema); CAD: Coronary Artery Disease; CD: Cardiac Dysrhythmia (arrhythmia) (types of
CD: 1=atrial, 2=junctional, 3=atrio-ventricular, 4=ventricular, 5=heart blocks).
13
Table 2. Inter-session Pearson’s correlation between AM and PM mean values of multiple
measurements per position per session per subject (UP: normal third trimester pregnant
women, PE: pre-eclamptic women, and CV: critically-ill cardiology patients) (SBP:
systolic blood pressure, DBP: diastolic blood pressure, MAP: mean arterial pressure, PP:
pulse pressure, HR: heart rate, HPD: heart period duration, PEP: pre-ejection period,
LVET: left ventricular ejection time , STR: systolic time ratio, ETR: ejection time ratio,
SV: stroke volume, SI: stroke index, CO: cardiac output, CI: cardiac index, ACI:
acceleration index, VI: velocity index, HI: heather index, O/C-ratio, TFC: thoracic fluid
content, TFCI: TFC index, TAC: total arterial compliance, TACI: TAC index).
AM vs PM
Mean values
Pressures
Time periods
Volumes
CV
A
B
C
D
A
B
C
D
A
B
C
D
(mmHg)
0.72
0.41
0.84
0.91
0.67
0.83
0.73
0.60
0.68
0.71
0.48
0.37
DBP
(mmHg)
0.75
0.72
0.69
0.76
0.49
0.37
0.66
0.45
0.63
0.68
0.59
0.81
MAP
(mmHg)
0.85
0.82
0.84
0.83
0.41
0.65
0.69
0.48
0.37
0.65
0.53
0.23
PP
(mmHg)
0.46
0.25
-0.01
0.88
0.60
0.71
0.82
0.60
0.90
0.82
0.76
0.85
HR
(1/min)
0.84
0.38
0.51
0.68
0.77
0.44
0.72
0.61
0.94
0.86
0.86
0.85
0.72
0.74
0.41
0.74
0.51
0.89
0.85
0.84
0.90
HPD
(ms)
0.83
0.46
0.48
PEP
(ms)
0.47
0.25
-0.01
0.88
0.94
0.88
0.57
0.91
0.49
0.71
0.85
0.77
0.18
0.83
0.76
-0.01
0.58
0.00
0.73
0.43
0.46
0.79
0.62
0.74
STR
0.62
0.79
0.71
-0.22
0.71
0.59
0.55
0.63
0.14
0.69
0.69
0.69
ETR (%)
0.52
0.69
0.94
-0.27
0.43
0.49
0.74
0.12
0.73
0.88
0.63
0.82
SV
(ml)
0.64
0.79
0.82
0.63
0.85
-0.22
0.74
0.56
0.93
0.89
0.94
0.91
(ml/m²)
0.60
0.84
0.86
0.67
0.82
0.08
0.82
0.60
0.92
0.86
0.90
0.90
(l/min)
0.75
0.70
0.93
0.34
0.82
0.65
0.69
0.43
0.97
0.87
0.90
0.95
(l/min/m²)
0.68
0.67
0.94
0.37
0.75
0.41
0.66
0.39
0.97
0.85
0.90
0.94
0.90
0.84
0.97
0.93
0.85
0.92
0.89
0.82
0.94
0.94
0.92
0.89
(1/1000/s)
0.94
0.96
0.98
0.95
0.95
0.96
0.95
0.95
0.93
0.95
0.95
0.89
(Ohm/s²)
0.85
0.86
0.92
0.88
0.93
0.90
0.93
0.94
0.93
0.94
0.93
0.93
0.26
0.52
0.57
0.60
0.31
0.71
0.54
0.67
0.74
0.24
0.90
0.74
(1/kOhm)
0.85
0.97
0.97
0.92
0.97
0.95
0.96
0.95
0.63
0.94
0.72
0.70
(1/kOhm/m²)
0.90
0.98
0.98
0.94
0.97
0.95
0.96
0.96
0.67
0.95
0.77
0.74
(ml/mmHg)
0.60
0.76
0.30
0.72
0.85
0.67
0.86
0.42
0.75
0.85
0.85
0.81
(ml/m²/mmHg)
0.67
0.76
0.49
0.78
0.83
0.69
0.88
0.46
0.71
0.82
0.83
0.81
LVET
SI
CO
ACI
VI
(ms)
(1/100/s²)
HI
O/C (%)
TFC
Resistance
PE
SBP
CI
Contractility
UP
TFCI
TAC
TACI
14
Table 3. Intra-session Pearson’s correlation between mean values of multiple
measurements per subject in supine 1 and supine 2 positions within AM or PM sessions
(UP: normal third trimester pregnant women, PE: pre-eclamptic women, and CV:
critically-ill cardiology patients) (SBP: systolic blood pressure, DBP: diastolic blood
pressure, MAP: mean arterial pressure, PP: pulse pressure, HR: heart rate, HPD: heart
period duration, PEP: pre-ejection period, LVET: left ventricular ejection time , STR:
systolic time ratio, ETR: ejection time ratio, SV: stroke volume, SI: stroke index, CO:
cardiac output, CI: cardiac index, ACI: acceleration index, VI: velocity index, HI: heather
index, O/C-ratio, TFC: thoracic fluid content, TFCI: TFC index, TAC: total arterial
compliance, TACI: TAC index).
Supine 1 vs supine 2
Mean values
Pressures
Time periods
Volumes
CV
AM
PM
AM
PM
AM
PM
SBP
(mmHg)
0.94
0.89
0.60
0.83
0.77
0.94
(mmHg)
0.86
0.86
0.92
0.40
0.79
0.72
MAP
(mmHg)
0.88
0.93
0.93
0.63
0.57
0.17
PP
(mmHg)
0.85
0.83
0.29
0.47
0.85
0.94
HR
(1/min)
0.81
0.88
0.92
0.92
0.97
0.93
HPD
(ms)
0.83
0.87
0.94
0.89
0.95
0.94
PEP
(ms)
0.96
0.23
0.91
0.94
0.87
0.73
0.41
0.80
0.70
0.72
0.58
0.92
STR
0.78
0.38
0.69
0.87
0.65
0.67
ETR (%)
0.45
0.63
0.57
0.57
0.77
0.78
SV
(ml)
0.47
0.96
0.78
0.89
0.96
0.98
(ml/m²)
0.47
0.97
0.84
0.89
0.96
0.98
(l/min)
0.42
0.92
0.75
0.82
0.96
0.98
(l/min/m²)
0.39
0.92
0.79
0.80
0.95
0.97
0.96
0.93
0.96
0.98
0.95
0.94
(1/1000/s)
0.97
0.95
0.98
0.99
0.99
0.97
(Ohm/s²)
0.96
0.95
0.95
0.96
0.97
0.96
0.51
0.86
0.83
0.67
0.72
0.71
LVET
SI
CO
CI
VI
(ms)
(1/100/s²)
HI
O/C (%)
TFC
Resistance
PE
DBP
ACI
Contractility
UP
(1/kOhm)
0.96
0.98
0.99
0.98
0.95
0.99
(1/kOhm/m²)
0.98
0.99
0.99
0.98
0.96
0.99
(ml/mmHg)
0.75
0.86
0.66
0.65
0.79
0.82
(ml/m²/mmHg)
0.79
0.90
0.65
0.66
0.79
0.80
TFCI
TAC
TACI
15
Figures
Figure 1. Measurement protocol in which blood pressure is taken every two minutes. A
calibration period (c) is present before the new blood pressure value is depicted on the
screen. The time period during position change is highlighted in black. Data is collected
over a timespan of one minute. BP: Blood Pressure.
16